Imperial shag

Published on August 15, 2015

Profile

The imperial shag is a medium sized bird living in and around Antarctica. Males and females look a lot alike, both have a black back and a white belly. Some distinguishing features of this birds are the blue around their eyes and the orange-brown knobs above their beaks. These knobs are called caruncles. The imperial shag is a type of cormorant, but unlike other cormorants, it does not spread its wings to dry after diving. This is because this bird lives in a cooler climate than other cormorants, and drying its wings that way would draw heat from the bird’s body. Imperial shags have denser bones than most sea birds. This probably helps them stay under water while chasing prey. These birds have many different names. I won’t bore you with all of them, but here are a few: Blue eyed cormorant, King cormorant, Heard shag, Heard island cormorant, King shag, and White bellied cormorant. Despite the name “Blue-eyed cormorant” and the fact that it looks like the birds in the picture above have blue eyes, they actually have brown eyes. The blue you see is actually skin around the eyes.

Range

These birds live around the Atlantic Ocean near South America and Antarctica. They also inhabit the southern Indian Ocean. Some of the notable islands they call home include the Falkland Islands, Heard Island, and the South Sandwich Islands. They also live on the peninsula of Antarctica.

Size

Adult imperial shags reach a length of 26 to 30 inches (68-76 cm). They have a wingspan of about 47 inches (120 cm). Imperial shags can weigh up to 6.6 pounds. Males are slightly larger than females.

Diet and hunting

Unlike most other birds (a notable exception being penguins), imperial shags are good swimmers. They catch their prey after pursuing it under water. Many other sea birds will dive down from the air and immediately attack their prey. You can tell from these hunting habits that their prey must be aquatic. Their food includes fish, squids, and other mollusks. These birds are able to stay under water for up to four minutes at a time. They are able to do this because their bodies have a lot of blood in them, and they therefore can have a large amount of oxygen stored in their blood. Normal dives go down to about 82 feet (25 m) when catching prey, but they are able to dive up to 328 feet (100 m) below the surface! They have special inner feathers that insulate against cold and water. Water does stick to their outer feathers, however. Because of this, they are only able to go hunting for an hour before returning to land to let their feathers dry. When feeding, they do so individually or sometimes they flock with numbers in the thousands.

Status and threats

The IUCN Redlist classifies the Imperial shag as Least Concern. This bird has a range that is far from human activity, so there are not a lot of human threats. Adults have no natural predators, but unguarded eggs and young can fall prey to skuas and gulls. They have never been hunted extensively by humans. Some small populations on the Heard Islands are vulnerable to extreme weather that may destroy nests. Marine pollution and debris can also kill birds. Although there are no known conservation measures directed specifically at blue-eyed cormorants, they do benefit from other undertakings. Attempts to restore seabird habitat and remove invasive predators help these birds.

Mating, eggs, and young

When breeding, these birds form colonies of several hundred thousand birds! Pairs frequently change their nesting sites between seasons. Their is fierce competition surrounding the best nesting sites, yet the fights rarely go beyond threatening posture. Occasionally males will “joust” with their bills and grab each other’s wings and necks. Males build the cup-shaped nest with vegetation, mud, and bird droppings they find around the colony. Females lay a clutch of normally three eggs, and over the next around 28 days, both the male and the female incubate the eggs. The chicks hatch with no feathers, but due to their energy-rich diet of fish, they will be able to fly after 75-80 days. Juveniles do not have the blue skin around their eyes or the orange caruncles. Their average lifespan is unknown or not widely stated.

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